Beryllide coating for beryllium



1967 c. J. SPEERSCHNEIDER 3,297,417

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To m m BY 5.49m; 80 T0 m M TO N: (Ag PLATED) DIFFUSION COUPLES dffdPd/EVUnited States Patent 0 3,297,417 BERYLLEDE CSATING FDR BERYLLlUP/lCharles J. Speerschneider, Minnetonka, Minn, assignor to Honeywell line,a corporation of Delaware Filed Mar. 26, 1964. Ser. No. 354,9ll4 8Claims. (Cl. 29199) Generally, this invention is directed to lowfriction, wear re 'stant coatings for beryllium. More specifically, thisinvention is concerned with a beryllide intermetallic coating forberyllium and a method for preparing such coatings.

Beryllium has achieved widespread use due to its low density andrelatively high strength. It has found particular application in gasbearing structures as a basic material. However, this use has been quitelimited since beryllium has poor resistance to Wear and a high CO-efiicient of friction. Consequently, a low friction, wear resistantadherent coating for the beryllium is necessary.

Hard ceramic materials have been used previously as a coating forberyllium to obtain improved resistance to wear over the basic berylliummaterial. One technique used to obtain such coatings has been the flamespray ing of beryllium with materials such as alumina. These coatingsresult in relatively good resistance to wear, however, they are porousand thus undesirable from a bear ing dynamics standpoint. Also, thishard surfacing material is sprayed directly onto the beryllium surfacewith no transition zone between the relatively soft beryllium and therelatively hard ceramic. A transition zone is desirable since it resultsin a gradual change in proper-fies reducing the stress concentrationsand increasing adhesion. A second technique which has been utilized isan anodizing procedure. However, again porosity is present in additionto processing difficulties in controlling beryllium oxide coatings.

It has been found that surface coatings of. gammanickel beryllide (M 86having substantial thickness can be applied to both flat and cylindricalberyllium surfaces using a diffusion technique. The coatings are veryhard. have a high surface density (non-porous) and are adherent to theberyllium base material. Good adhesion is due to the formation of a twophase transition region between the gamma-nickel beryllide and theberyllium. In order to obtain this two phase region a third element,silver, is necessary and is best introduced as an alloying agent in theberyllium.

It is an object of this invention to improve beryllium for use as abearing material, particularly in gas bearing applications.

It is another object of this invention to provide a low friction, wearresistant coating for beryllium having good adherence due to thepresence of a two phase transition region.

It is a further object of this invention to provide a low friction, wearresistant coating for beryllium which has a high surface density, i.e.,a non-porous coating.

It is another object to provide a beryllide coating for beryllium havinga hardness which is comparable to coatings used in the prior art andwhich has excellent adherence to the beryllium base material.

It is a still further object of the invention to provide a diffusionbonding method for preparing beryllide coatings on beryllium whichresults in a coating having superior properties over those of the priorart.

It is another object to provide a diffusion bonding method for preparingberyllide coatings on beryllium in which relatively thick coatings canbe prepared in a short time.

It is still another object to provide a method for EQWAW Patented Jan.19, 1967 in highly adherent coatings due to the formation of a two phasetransition region in the coating.

it is a still further object to provide a novel method for preparingberyllide coatings on beryllium which utilizes silver to form a twophase transition region in the coating.

These and other objects and advantages of the present invention willbecome evident from the following description in which:

FIGURE 1 is a schematic representation of a diffusion couple of nickeland beryllium showing the various regions formed therebetween as aresult of heating.

FIGURE 2 is a graph showing the shear strength and fracture path ofvarious diffusion couples.

FIGURE 3 is a graph showing the effect of time, temperature and silveralloy content on total beryllide thickness.

Briefly, the beryllide intermetallic coating prepared in accordance withthis invention is composed of two regions (1) gamma-nickel beryllide (NiBe and (2) a two phase region of gamma-nickel beryllide plus aberylliumsilver alloy (Ni Be +BeAg). These regions are formed by adiffusion bonding technique. The technique involves the contacting of aberyllium base material by a body of nickel and a subsequent heattreatment. In order to obtain the desired two phase transition regionbetween the nickel beryllide (Ni Be and the beryllium, a third elementis necessary. This is silver which may be introduced in various ways aswill be discussed hereinbelow. After introduction of the silver, heatingforms a diffusion bond between the nickel and beryllium as shownschematically in FIGURE 1. This type of structure is termed a diffusioncouple and is composed of live regions;

Region Anickel Region BNiBe (5) Region C-Ni Be ('y) Region DNi Be-l-BeAg (two phase) Reg on Eberyllium or berylliumsilver Subsequent tothe diffusion bonding, regions A and B are removed by grinding or thelike to expose the gammanickel beryllide of region C thus providing atwo layer beryllide coating for the beryllium base material.

Procedure The method used in diffusion bonding begins with the cleaningof the beryllium base material and the nickel material by standardprocedures which are well known in the art such as abrading the surfaceswith a fine grit. The two bodies are then placed in contact under alight load (sufiicient to maintain contact between the work pieces) andheated in a vacuum. For curved surfaces, a molybdenum sleeve with itslow coefiicient of thermal expansion is used to maintain intimatecontact at elevated temperatures Whereas a very light, dead weight loadis used with diffusion couples of the type shown in FIGURE 1. Theapplied temperature has been found to be critical in that it must be atleast about 1075 C. to obtain bonding through formation of the two phaseregion. Higher temperatures are limited only by the fact that theyshould not exceed the melting point of the beryllium. A preferredtemperature range has been found to be about 1100 C. and above due toincreasing hardness and thickness of the coating produced withincreasing temperatures. A heating time of at least /2 hour is requiredto form the desired diffusion region.

Silver As previously Stated, the presence of silver is required toobtain the two phase region designated as D in FIG- URE l. The two phaseregion provides a transition zone from the relatively soft beryllium tothe extremely hard gamma-nickel beryllide (Ni Be A transition zone isnecessary since it allows for a gradual change in properties thusreducing stress concentration and increasing adhesion. This is confirmedby the fact that, in dilfusion couples prepared in the same way asdiscussed above, but without added silver, the two phase region wasabsent and the couples separated during handling.

The silver may be introduced into the diffusion couple in many ways.Plating either the nickel or beryllium with silver or inserting a thinsheet of silver between the two bodies prior to heating has been foundto produce the desired results. A silver plate formed on the nickel bodywhich is then placed in contact with the beryllium and bonded has beenfound to be particularly satisfactory. The amount of the silver plateentering into the reaction is determined by the temperature to which thecouple is heated since the solubility of the silver is dependent ontemperature.

An alternate approach for including the silver is to incorporate itdirectly into the beryllium base material. This is accomplished bystandard powder metallurgy techniques. The most satisfactory resultshave been obtained when an alloy has been used consisting of 18% silver,balance beryllium.

Adherence A measure of the shear strength of sample berylliumnickeldiffusion couples shows that strength varies with alloy addition from6000 p.s.i. for beryllium-8% silver to 2800 p.s.i. for beryllium-1%silver. FIGURE 2 shows how the shear strength of the beryllium-nickeldiffusion couples varies with silver additions from 6000 p.s.i. forberyllium-8% silver and silver plated nickel (excessive silver) to 2800p.s.i. for beryllium-1% silver. More important, an examination of thefracture path in the var ious samples as noted in FIGURE 2 shows thatfor the beryllium-8% silver alloy, fracture occurs either within thegamma-beryllide layer or at the nickel-beta-beryllide interface; whereasfor the beryllium-1% silver the fracture path is entirely within theberyl-ium-gamrna-beryllide interface. The increase in silver from 1% to8% or in the case of silver plated nickel (which is excessive silver)raises the beryllium-grimmaberyllide interface strength to aboveapproximately 6000 p.s.i. making it stronger than the gamma-beryllidelayer of the nickel-beta-beryllide interface.

Hardness The hardness of gamma-nickel beryllide (Ni lie il is about 1300(diamond pryamid number) which compares quite favorably with alumina(1200). The two phase transition region (Ni Be beryllium-silver) whichlies between the very hard gamma-nickel beryllide and the beryllium hasa hardness of 600. Representative microhardness values for a number ofcompounds applicable as coatings for beryllium are shown in Table I. Theberyllium compounds listed in the table were formed at about 1100 C. Forthe beryllide it was found that the presence of silver does not affecthardness although its presence is a critical factor in achievingadherence. However, it appears that there is a critical temperaturewhich must be achieved to obtain high hardness values in the berylliumcompounds as those compounds formed at 1000 C. do not have a highhardness.

Table I.-Micrlzrzrdness values Hardness Material: (diamond pyramid No.)NlBe21 A1 0 1200 NiBe 675 4 Thickness Relatively thick berylide layerscan be formed in a short time in accordance with this invention. Fore:\'- ample, at 1100 C. with a beryllium-4% silver alloy an 0.030 inchlayer is formed in about 3 hours. FIGURE 3 shows the total beryllidethickness formed for the various alloys as a function vof diffusion timeat 1000 C. to 1100" C. The thickness increases as would be expected withtime and temperature. It is noted that silver content also has thiseffect which appears due to an indirect increase in temperature sincethis addition lowers the melting temperature of the alloy formed. Ofcourse, the ultimate thickness of any particular coating is dependent onthe particular use or application desired.

Although the invention has been shown and described in terms ofparticular embodiments, it will be appreciated that various changes andmodifications are conceivable which do not depart from its spirit andscope. Maximum hardness is achieved with pure gamma-nickel beryllide,however, slight deviations from this stoichiometric relationshipare-deemed to be within the scope of this invention. Accordingly, suchchanges and modifications as are obvious to one skilled in the art arealso deemed to be within the scope of the invention.

What is claimed is:

1. An article comprising: a beryllium body having thereon in adherentrelationship a wear resistant coating composed of first and secondregions, said first region comprising a two phase composition of aberyllium-silver alloy and gamma-nickel beryllidc, said second regioncomprising gamma-nickel beryllide.

2. An article comprising: a body, the composition of which is at leastsubstantially beryllium, having thereon in adherent relationship a wearresistant coating composed of first and second regions, said firstregion comprising a two phase composition of a beryllium-silver alloyand gammanickel beryllide, said second region comprising gamma-nickelberyllide.

3. An article comprising: a body, the composition of which is about 1%to about 8% silver, balance beryllium, said body having thereon inadherent relationship a wear resistant coating composed of first andsecond regions, said first region comprising a two phase composition ofa beryllium-silver alloy and gamma-nickel beryllidc, said second regioncomprising gamma-nickel beryllide.

The method of forming a beryllide coating on a beryllium body comprisingthe steps of:

(A) diffusion bonding a nickel body in the presence of silver to saidberyllium body at a temperature of at least about 1075 C. for a timesulficient to form a diffusion couple consisting of discrete regions ofnickel, betanickel beryllidc, gammanickel beryllidc, a two phase regionof a beryllium-silver alloy plus gamma-nickel'beryllide and a region ofberyllium, and

(B) removing said nickel and beta-nickel bcryllide regions to exposesaid gamma-nickel beryllide region as an outer coating on said berylliumbody.

5. The method of forming a beryllide coating on a beryllium bodycomprising the steps of:

(A) positioning said beryllium body in bonding relationship with a bodyof nickel,

(B) inserting an amount of silver between said bodies,

(C) heating said bodies in a vacuum to a temperature of at least aboutl075 C. for at least /2 hour to form a diffusion couple therebetweenconsisting of discrete regions of nickel, beta-nickel beryllidc, gamrna-nickel beryllidc, a two phase region of a beryllium-silver alloyplus gamma-nickel beryllidc, and a beryllium region, and

(D) removing said nickel and beta-nickel beryllide regions to exposesaid gamma-nickel beryllide region as an outer coating on said berylliumbody.

6. The method of forming a beryllide coating on a beryllium bodycomprising the steps of:

(A) contacting said beryllium body with a nickel body having a silverplate thereon,

(B) heating said bodies to a temperature of at least about 1075 C. forat least /2 hour to form a diffusion couple consisting of discreteregions of nickel, beta-nickel beryllide, gamma-nickel beryllide, a twophase region of a beryllium-silver alloy plus gammanickel beryllide, anda reg-ion of beryllium, and

(C) removing said nickel and beta-nickel beryllide region to exposedsaid gamma-nickel :beryllide as an outer coating :bonded to saidberyllium body by said two phase region.

7. The method of forming a gamma-nickel beryllide coating bonded to abody consisting substantially of beryllium by means of a two phasetransition region comprising the steps of:

(A) providing a body of a beryllium-silver alloy,

(B) contacting said body with a nickel body,

(C) heating said bodies at a temperature of at least about 1075 C. forat least /2 hour to form a diffusion couple consisting of discreteregions of nickel, beta-nickel beryllide, gamma-nickel beryllide, a twophase region of a beryllium-silver alloy plus gamma-nickel beryllide andsaid beryllium-silver alloy, and

(D) removing said nickel and beta-nickel beryllide regions to exposesaid gamma-nickel beryllide as an outer coating bonded to saidberyllium-silver alloy by said two phase region.

8. The method of forming a gamma-nickel beryllide coating bonded to aberyllium-silver alloy body by a two phase transition region comprisingthe steps of:

(A) providing a body of a beryllium-silver alloy containing from about1% up to about 8% silver, balance beryllium,

(B) contacting said :body with a nickel body,

(C) heating said bodies at a temperature of at least about 1070 C. forat least /2 hour to form a diffusion couple consisting of discreteregions of nickel, beta-nickel beryllide, gamma-nickel beryllide, a twophase region of a beryllium-silver alloy plus gammanickel beryllide andsaid beryllium-silver alloy and (D) removing said nickel and beta-nickelberyllide regions to expose said gamma-nickel beryllide region as anouter coating bonded to said berylliumsilver alloy by said two phaseregion.

References Cited by the Examiner UNITED STATES PATENTS 2,846,792 8/1958\Valker et al. 29l94 2,969,309 1/1961 Finniston et al. 29--194 3,044,1567/1962 Whitfield et a1. 29194 3,082,521 3/1963 Cohen 75150 DAVID L.RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

R. O. DEAN, Assistant Examiner.

1. AN ARTICLE COMPRISING: A BERYLLIUM BODY HAVING THEREON IN ADHERENTRELATIONSHIP A WEAR RESISTANT COATING COMPOSED OF FIRST AND SECONDREGIONS, SAID FIRST REGION COMPRISING A TWO PHASE COMPOSITION OF ABERYLLIUM-SILVER ALLOY AND GAMMA-NICKEL BERYLLIDE, SAID SECOND REGIONCOMPRISING GAMMA-NICKEL BERYLLIDE.